The present invention relates to a pneumatic tire having an improved airtight layer capable of reducing tire weight.
In recent years, from an environmental aspect, pneumatic tires are required to reduce their weight. Therefore, various proposals were have been made. For example, the laid-open Japanese patent applications JP-A-H06-156007 and JP-A-H08-113007 disclose a pneumatic tire wherein, a cord ply rubberized with an air-impermeable rubber compound is used in the carcass, and the conventional inner liner is eliminated. The tire weight is therefore, reduced accordingly,
In practice, however, it is very difficult to uniformly reduce the thickness of rubber inside the carcass because during the vulcanization of the tire, the tire inner surface is pressed by an inflated bladder and the bladder rubs the inside of the carcass ply. If the bladder touches the carcass cords, the carcass cords are exposed, and not only the airtightness but also the resistance to humidity is decreased causing a deterioration in the durability.
Therefore, a principal object of the present invention is to provide a pneumatic tire in which, in order to reduce the tire weight, the rubber thickness of an airtight layer disposed along the inner surface of the tire is minimized uniformly, without creating defects such as breakage.
Another object of the present invention is to provide an improved airtight layer capable of minimizing its thickness without sacrificing its airproofing power.
According to the present invention, a pneumatic tire is provided which comprises a tread portion, a pair of sidewall portions, a pair of bead portions, a carcass comprising a ply of cords defining the innermost reinforcing cord layer extending between the bead portions, and an airtight layer disposed along the inner surface of the tire, covering substantially the entire inner surface of the tire, the airtight layer being made of an air-impermeable rubber including at least 10 weight % of a halogenated butyl rubber and/or a halogenated isobutylene-paramethyl styrene copolymer in its rubber base, and having a thickness of the airtight layer measured from the inner surface of the tire to the cords of the carcass ply in a range of from 0.2 to 0.7 mm.